A steam autoclave for sterilizing purposes consists of a chamber with steam inlets and condensate outlets as well as other necessary connections for vacuum etc. Often a jacket is provided for temperature control, the jacket having connections for steam supply, condensate removal, vacuum and venting. An autoclave or steam sterilizer as described may go through a number of operational phases during use, like charging a load, removing the air, heating up to a temperature, exposing the load to the temperature and sterilization media, cooling and discharging the load, with several cycle variations.
Heating up is carried out with steam acting directly on the load in the chamber. Prior to the heating up stage, air is removed from the chamber by pulling a vacuum in the chamber and replacing it with steam. Several repetitions of this cycle may be carried out. To minimize condensation on the chamber walls, the jacket may be steam heated. Condensate is usually collected at the side(s) of the jacket, normally so that a small amount of condensate is left on the bottom of the chamber.
Cooling is typically carried out by filling the jacket with cold water and allowing a flow until the desired temperature is reached. The water consumption during this stage is significant.
As explained above, a vacuum system is conventionally provided in steam autoclave systems, usually served by a water ring pump. A water ring pump (in this context, the expression “liquid ring pump” is equivalent to “water ring pump”) is a device in which a vaned impeller rotates to form a moving cylindrical body of liquid, which forms the seal of a series of compression chambers formed by the space between the vanes. The eccentric placement of the impeller within the pump housing gives rise to a cyclic variation in the volume enclosed by the vanes and the water ring. The ring liquid is partly entrained with the discharge stream, and must be replaced by fresh makeup liquid or with cooled and recycled liquid separated from the discharge stream.
Since a water ring pump can draw gas-liquid mixtures without problems, they are well suited for autoclave service. The vacuum obtainable with a liquid ring pump is dependent on the vapor pressure of the liquid in question at the operating temperature. To maintain the vacuum capacity, the liquid must often be cooled.